Drive mechanism for photsensitive web in an image transfer type electrophotographic copier

ABSTRACT

An apparatus comprising a photosensitive element made of a flexible sheet to be moved reciprocally for each image transfer cycle, a suction box fixedly supporting one end of the photosensitive element at its inlet portion and subjected to a reduced pressure in its interior by pressure reducing means to draw in the photosensitive element along its inner wall and to thereby tension the element to a planar form at an exposure station, and drive means for defining the path of advance of the photosensitive element and defining the direction of movement of the same.

United States Patent [191 Tanaka et al.

DRIVE MECHANISM FOR PHOTSENSITIVE WEB IN AN IMAGE TRANSFER TYPEELECTROPHOTOGRAPHIC COPIER Inventors: Susumu Tanaka, Sakai; YujiEnoguchi, Higashiosaka; Takao Fujiwara, Sakai, all of Japan MinoltaCamera Kabushiki Kaisha, Osaka, Japan Filed: Jan. 24, 1973 Appl. No.:326,360

Assignee:

Foreign Application Priority Data Feb. 7, 1972 Japan 47-13699 US. Cl355/16, 355/8, 355/15 Int. Cl G03g 15/00 Field of Search 355/16, 11, 8,3

References "Cited UNITED STATES PATENTS Morse 355/16 Apr. 30, 19743,697,160 10/1972 Clark 355/16 3,646,866 3/1972 Baltazzial 355/16Primary ExaminerRichard L. Moses Attorney, Agent, or FirmWolder & Gross[57] ABSTRACT An apparatus comprising a photosensitive element made of aflexible sheet to be moved reciprocally for each image transfer cycle, asuction box fixedly supporting one end of the photosensitive element atits inlet portion and subjected to a reduced pressure in its interior bypressure reducing means to draw in the photosensitive element along itsinner wall and to thereby tension the element to a planar form at anexposure station, and drive means for defining the path of advance ofthe photosensitive element and defining the direction of movement of thesame.

14 Claims, 7 Drawing Figures PATENTEDAPR 30 m4 SHEET 1 (IF 3 Fig.7

BACKGROUND OF THE INVENTION The present invention relates toelectrophotographic copiers of the image transfer type, moreparticularly to an apparatus for driving a photosensitive element to beused repeatedly in electrophotographic copiers of the image transfertype such as the electrostatic latent image transfer type, powder imagetransfer type and the like.

The photosensitive element used in electrophotographic copiers of theimage transfer type has a photoconductive film which iselectrostatically charged by a charger and then exposed to reflectedlight from the surface of document to form the image of the document asan electrostatic latent image. Suchphotoconductive film is generallyadhered to a drum or belt for repeated use. When the photosensitiveelement gets deteriorated due to repeated use over a long period, thephotosensitive element has to be replaced along with the drum or belt.The replacing procedure is therefore very cumbersome and expensive.

In recent years, it has been proposed to use a flexible photosensitiveelement in the form of a roll as disclosed in US. Pat. No. 3,588,242 byR. A. Berlier et al. and in Publication of Japanese Patent applicationNo. 41356/1971 by K. Amemiya, the roll of photosensitive element beingsuch that the deteriorated portion thereof will be wound up to pay out afresh portion for use.

According to the US. Pat. No. 3,588,242, a drum of a large diameter forproviding the photosensitive element on its surface has in its interiora supply roll and a takeup roll, and the photosensitive element wound onthe.supply roll is paid out over the drum surface, with the leader endof the element wound on the takeup roll. When the photosensitive portionon the drum surface has been deteriorated, the deteriorated portion iswound up on the takeup roll to pull out a fresh photosensitive portion.The photosensitive element extending around the drum surface issubjected all the time to mechanical tension exerted by the takeup roll.The photosensitive elementof this apparatus is driven by the rotation ofthe drum to pass through a corona unit, exposure station, developingunit and transfer station which are disposed around the drum for thetransfer copying operation already known.

According to the Publication of Japanese Pat. application No.41356/1971, a roll of flexible photosensitive element is paid out from asupply roll and the leader end is wound on a takeup roll, thephotosensitive element extending between the two rolls in a taut planarfashion. If the extending portion gets deteriorated, the deterioratedportion is wound up on the takeup roll to pull out a fresh portion fromthe supply roll for use. The photosensitiveelement is always subjectedto mechanical tension, with the two rolls kept spaced apart by aconstant distance, and the rolls and the photosensitive elements in thisstate are moved reciprocally in a horizontal direction. Various meansfor transfer copying operation are disposed in series along the path ofthe reciprocation to conduct the copying operation already known.

The two examples described have the drawback that the photosensitiveelement is susceptible to fatigue due to stress, hence a short servicelife and marked wear of the element inasmuch as the flexiblephotosensitive element is subjected to mechanical tension all the time.Moreover, since the photosensitive element is driven on the support drumor is reciprocated over a distance several times the space between therolls while being supported on the rolls, the construction requires alarge space for driving the photosensitive element, making the copiergreater in size to occupy an increased floor space.

SUMMARY OF THE INVENTION An object of this invention is to subject aflexible photosensitive element to a minimum of requisite tension whenit is driven reciprocally for a transfer copying operation so as to keepthe element planar at the exposure station and to thereby prevent theshortening'of its service life and cost increase due to its wear.

Another object of this invention is to simplify the construction of amechanism for driving the photosensitive element to the greatestpossible extent and to reduce the space volume required for driving thephotosensitive element so as to provide a compact electrophotographiccopier of the type described.

Still another object of this invention is to provide an apparatus of avery simple construction capable of returning the photosensitive elementquickly for reciprocation.

To fulfil these objects, the apparatus of this invention ischaracterized by suction means for moving the photosensitive elementalong its inner wall by drawing the same in one direction so as tosubject the element to tension and means for defining the direction ofmovement of the photosensitive element.

According to our experiment,the suction to be exerted on thephotosensitive element to keep the same planar at the exposure stationis given by suction means which produces a very low negative pressure ofthe order of 30 mm Aq'. and it has become possible to greatly reduce thetension on'the photosensitive element as compared with the knownapparatus, this consequently making it possible to materially reduce thestress to be produced in the photosensitive sensitive element by thetension. Moreover, the invention simplifies the mechanism for drivingthe photosensitive element and reduces the space volume required for thereciprocation of the element.

Other objects and features of this invention will become more apparentfrom the following description of embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partly in verticalsection showing the principal part of an embodiment of this invention;

FIGS. 2(a) and (b) are views illustrating the operation of aphotosensitive element in the embodiment of FIG. 1;

FIG. 3 is a view partly in vertical section showing the principal partof another embodiment of this invention;

FIG. 4 is a view partly in vertical section showing the principal partof another embodiment of this invention; and

FIGS. (a) and (b) are views illustrating the operation of aphotosensitive element in the embodiments of FIGS. 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows anelectrophotographic copier of the electrostatic latent image transfertype. A document table 1 made of a transparent material such as a glassplate is fixedly positioned at the top of a frame A. A document B to becopied is placed face down on the table 1 and is illuminated by a lamp Lof an illuminating system 2.

The illuminating system 2 has a first movable system comprising the lampL and a reflecting mirror M 21 second movable system comprisingreflecting mirrors M and M a stationary system comprising animageforming lens 3 and a reflecting mirror M and an exposure slit 4 forprojecting the reflected light from the surface of the document to anexposure station E. As described in detail in Japanese Pat. PublicationNo. 6647/ 1 964, the first movable system travels at a velocity of vwhile the second movable system travels at a velocity of v/2 so that thereflected light from the surface of the document illuminated by the lampL is projected, by means of the first and second movable systems and thereflecting mirror and lens of the stationary system, onto a flexiblephotosensitive element P moving at the same velocity v in synchronismwith the first movable system so as to form an electrostatic latentimage on the photosensitive element P.

A suction box 5 has at its one end an inlet portion 5a where a stockroller 6, serving to fix one end of the photosensitive element P, isremovably mounted. The suction box 5 has at the'other end thereof anexhaust fan 7 or like suction means, with cloth 5b such as siliconecloth adhered to the inner surface of the box.

The flexible photosensitive element P has one end se cured to the stockroller 6 and the other end secured to a take-up roller 8 which is alwaysurged by an unillustrated spiral coiled spring or the like toward adirection to wind up the photosensitive element P. A guide roller 9positioned between the stock roller 6 and the take-up roller 8 definesthe path of movement of the photosensitive'element. A drive roller 10 isout of contact with the'photosensitive face of the element P but is inelastic contact with the widthwise opposite edges of the element P orwith the opposite ends of the guide roller 9 and rotates the roller 9 todrive the photosensitive element P at the same velocity as the firstmovable system in synchronism with the exposure making operation of theilluminating system 2.

The drive roller 10 rotates in the normal direction to advance thephotosensitive element P in synchronism with the first movable systemand rotates in the reverse direction upon completion of a transferoperation to move the element P backward. Alternatively, upon completionof the transfer operation, unillustrated electromagnetic means orsuitable mechanical means may separate the drive roller 10 from thephotosensitive element P or from the guide roller 9 as shown in FIG.2(b) to permit the photosensitive element P to be returned by thesuction of the suction box 5.

In the case where a photosensitive element in the form of a roll isused, the stock roller 6 is formed with a cavity for accommodating theunused portion (with fresh photosensitive face) of the element and thetakeup roller 8 is formed with a cavity for housing the used portion(with deteriorated photosensitive face) of the photosensitive element.The rollers are provided with slits for paying out and for drawing inthe photosensitive element respectively, the slits having means forsecuring the opposite ends of the operative portion of thephotosensitive element respectively. When the operative portion (i.e.the portion in use) gets fatigued or deteriorated, the deterioratedportion is wound up into the take-up roller 8, with a freshphotosensitive portion paid out from the stock roller 6. Such windingand unwinding operations can be conducted by any desired meansautomatically or manually.

Disposed along the path of advance of the photosensitive element P are acharger 11 for charging the photosensitive element P electrostatically,the aforementioned exposure station E, a transfer belt 12 for movingcopy paper at the same speed as the photosensitive element in snug-fitpressing contact with the element so that an electrostatic latent imageformed on the surface of the photosesitive element by exposure may betransferred onto the copy paper, and transfer rollers 13 and 14supporting the belt 12. A roll of copy paper 15 is cut to apredetermined copy size by a cutter 16 and pressed by the belt 12against the surface of the photosensitive element P for the transfer ofthe electrostatic latent image.

The copy paper bearing the electrostatic latent image thereon isseparated from the photosensitive element P by a separator 17, led todeveloping means 18 for development, passed under a heater 19 by afixing belt 19a and sent out from the frame through a copy outlet 20.

The photosensitive element is driven in the following manner. When anunillustrated main switch is closed, the exhaust fan 7 is driven toexhaust the air from the suction box 5, with the result that thephotosensitive element P is drawn into the box along its inner wall asshown in FIG. 1 (by solid line) and FIG. 2(a) and thereby subjected topredetermined tension.

The document B is placed on the table 1 and an unillustrated startswitch is depressed, whereupon the lamp L is lighted and the first andsecond movable systems of the illuminating system 2 are initiated intotravel from the solid line position in FIG. 1 toward the broken lineposition while maintaining the aforesaid relationship therebetween. Atthe same time, the photosensitive element P is driven in synchronismwith the first movable system against the suction of the box 5. Thus thecharging, exposure and transfer of the image are conducted and theelement P is wound up on the takeup roller 8.

In the case where the copy is of a maximum size set for the copier ofFIG. 1, the image transfer operation will be completed upon the firstand second movable system and the photosensitive element P reaching thebroken line position of FIG. 1. At this time the photosensitive elementP has reached the broken line position of FIG. 1 (i.e. the positionshown in FIG. 2(b) Upon completion of the copying operation, the driveroller 10 is driven in the reverse direction to return thephotosensitive element P or, as shown in FIG. 2(b), the

2(a) by the suction of the box 5 against the biasing force acting on thetake-up roller 8. The biasing force of the spiral coiled spring actingon the take-up roller 8 is of course set at a lower level than thesuction of the I box 5. Further during the return movement of thephotosensitive element P, the transfer belt 12 is of course releasedfrom the photosensitive surface.

The first and second movable systems of the illuminating system 2 arereturned to the solid line position of FIG. 1 simultaneously with thecompletion of the image transfer operation or upon completion ofexposure.

If the copy size is smaller than the maximum size designed for thecopier, the movable systems and the photosensitive element are stoppedwhen they have travelled a distance corresponding to the smaller copysize before reaching the broken line position of FIG. 1 and are thenreturned to the respective solid line positions.

' The silicone cloth5b provided on the inner wall of the suction box 5serves to automatically clean the photosensitive surface of the elementP by sliding contact therewith during the movement of the element P,eliminating the need to incorporate a special cleaner in the copier tosimplify the construction. The cloth further serves to protect thephotosensitive surface from scratching.

If the photosensitive element P is adapted to be returned by the suctionof the box 5, it becomes possible to greatly simplify the mechanicalconstruction required for the quick return of the element P. The suctionbox prevents the lateral deflection of the photosensitive element withits side wall during the reciprocal movement of the element so as toenable the element to advance straight. The suction box 5 further servesto guide the photosensitive element with its upper wall and eliminatesthe vertical shake or the photosensitive element along with the guideroller 9.

If the stock roller 6 and the take-up roller 8 are designed to beremovably mounted in place, the assembly .of the rollers including theroll of photosensitive element P accommodated in the stock roller 6 maybe constructed in the form of a cassette, this making it possible toreplace the photosensitive element P very easily and quickly. Since thetension acting on the photosensitive element during the copyingoperation is very small, the element is almost free of fatique anddeterioration due to the tension. Thus one photosensitive surface isable to conduct several tens of thousands of copying cycles. If the rollof photosensitive element loaded in the stock roller is so adapted thata fresh photosensitive portion can be paid out when the preceedingportion gets fatigued, one roll of photosensitive element will be ableto perform hundreds of thousands of copying cycles, with troublesreduced for the replacement of the photosensitive element.

FIG. 3 shows an electrophotographic copier of the electrostatic imagetransfer type as described in which a suction box 30 has two reducedpressure chambers 31 and 32. A stock roller 6 is positioned at an inletportion 31a of the first reduced pressure chamber 31 and a take-uproller 8a is disposed at an inlet portion 32a of the second reducedpressure chamber 32. The rollers are removably but fixedly mounted inplace. In this embodiment, the take-up'roller 8a need not be providedwith a spiral coiled spring or the like for winding up the operativephotosensitive portion during the advance of the element as in theembodiment of FIG. 1. During the reciprocal movement of thephotosensitive element, the take-up roller 8a remains stationary againstrotation. The same parts as those shown in FIG. 1 are referred to by thesame reference numerals.

The suction box 30 is divided by a partition wall 30a into upper andlower sections, i.e. into the first reduced pressure chamber 31 andsecond reduced pressure chamber 32, and both chambers 31 and 32 aregiven suction by a common exhaust fan 7 through passages 31b and 32b.Cleaning cloth 320 such as silicone cloth is adhered to a portion to bein sliding contact with the photosensitive surface of the element P. Thestock roller 6 and the take-up roller 8a are disposed at the inletportions 31a and 32a of the first and second reduced pressure chambers31 and 32 respectively. The photosensitive element P held at itsopposite ends to the rollers 6 and 8a has a portion thereof to beexposed passed around guide rollers 9 and 21 and is driven forward by adrive roller 10. Between the guide rollers 9 and 21, the photosensitiveelement P is in contact with a transfer belt 12.

FIG. 4 shows the suction box 30 of FIG. 3 as it is incorporated in aframe A of an electrophotographic copier of the powder image transfertype to apply this invention to the copier. The parts similar I to thoseshown in FIG. 3 are referred to by the same reference numerals.

Disposed along the path of movement of the photosensitive element P area transfer charger 22 in place of the transfer belt of FIG. 3 and adeveloping and cleaning box 23 in place of the developing means. Thedeveloping and cleaning box 3 is supported on the frame A in upwardlyand downwardly movable manner. During the advance of the photosensitiveelement P, developing means 24 is rotated at the illustrated positionnear the path of movement of the photosensitive element P to supplytoner from a toner feeder 25 to the photosensitive element P to form anelectrostatic latent image on the photosensitive surface into a visualpowder image. The visual image is then transferred by the transfercharger 22 to copy paper. The copy paper with the transferred imagethereon is carried by a belt 26a to fixing means 26 for fixing and thensent out from the frame through the copy outlet 20.

During the backward movement of the photosensitive element P, thedeveloping and cleaning box 23 is moved upward as indicated by the arrowto bring a cleaner 27 to the path of movement of the photosensitiveelement P, and the cleaner 27 is driven to clean the photosensitivesurface. The dust is drawn into a dust box 29 by a dust fan 28.

The photosensitive element P in the embodiments of FIGS. 3 and 4 isdriven as illustrated in FIGS. 5(a) and (b).

As already described, the first chamber 31 and the second chamber 32 aregiven interior reduced pressure by the common exhaust fan 7 to draw inthe photosensitive element P along their inner walls. In the illustratedembodiments, the passage 31b between the first chamber 31 and theexhaust fan 7 is larger than the passage 32b between the second chamber32 and the exhaust fan 7 to give a greater suction to the first chamber31 than to the second chamber 32.

When the exhaust fan 7 is initiated into operation by depressing themain switch, the photosensitive element P is drawn into the firstreduced pressure chamber 31 as illustrated in FIG. (a) and is subjectedto tension in contact with the inner wall face thereof under the suctionof the first and second chambers 31 and 32.

The depression of the start switch causes the drive roller to rotate theguide roller 9, forcing the photosensitive element P to start from theposition of FIG. 5(a) against the suction of the first chamber 31,followed by exposure and image transfer as previously described. Uponcompletion of the transfer operation, the element P reaches the positionof FIG. 5(b) (if the copy size is maximum). More specifically, thephotosensitive element P is drawn into the second chamber 32 along itsinner wall. At this time, the photosensitive surface is cleaned by thecleaning cloth 32c.

Upon completion of the transfer operation, the drive roller 10 is drivenreversely or is released from the guide roller 9 as shown in thedrawing, whereupon the photosensitive element P is returned quickly fromthe position of FIG. 5(b) to the position of FIG. 5(c) inasmuch as thefirst chamber 31 has greater suction than the second chamber 32.

Although the foregoing construction is such that the passages 31b and32b are different in size so as to give different suctions to the firstand second reduced pressure chambers 31 and 32, the passages 31b and 32bmay alternatively be provided with a changeover valve or throttle valveto give greater suction to the second chamber 32 than to the firstchamber 31 during the advance of the photosensitive element P andfurther to give greater suction to the first chamber 31 than to thesecond chamber 32 during the backward movement of the element P. Thedrive roller 10 may then act simply to control the velocity of movementof the photosensi tive element P.

Although the foregoing embodiments have been described with respect toelectrophotographic copiers of the image transfer type in which thedocument is held stationary and the illuminating system is movable, thepresent invention can likewise be embodied in the type in which thedocument is movable. Such modification will be included within the scopeof this invention.

What is claimed is:

1. An electrophotographic copier of the image transfer type comprising:

a photosensitive element made of a flexible sheet to be used repeatedlyby being driven reciprocally for each image transfer cycle,

a suction box having means for securing one end of the photosensitiveelement to its inlet portion and subjected to a reduced pressure in itsinterior by pressure reducing means, the suction box being operable toexert suction on the photosensitive element to draw in the element alongthe inner wall of the box upon actuation of the pressure reducing meansand to thereby tension the element to a planar form at an exposurestation,

means for fixedly supporting the other end of the photosensitiveelement,

drive means for advancing the photosensitive element along apredetermined path extending through the exposure station,

means for electrostatically charging a face of the photosensitiveelement,

exposure means for forming an image of an original on the charged faceof the photosensitive element in the exposure station forward of thecharging means to form a latent electrostatic image of the original onthe photosensitive element face, and

means for transferring said latent electrostatic image from saidphotosensitive element to a substrate exposed to said latentelectrostatic image on said photosensitive element face, said chargingmeans, exposure means and transfer means being actuated during theadvance of the photosensitive element.

2. The electrophotographic copier as set forth in claim 1 wherein themeans for fixedly supporting the other end of the photosensitive elementcomprises a take-up roller so biased all the time as to wind up thephotosensitive element in a direction opposite to the direction ofsuction of the suction box.

3. The electrophotographic copier as set forth in claim 1 wherein themeans for fixedly supporting the other end of the photosensitive elementcomprises a second suction box having means for securing the other endof the photosensitive element to its inlet portion and subjected to areduced pressure in its interior by pressure reducing means for exertingsuction on the photosensitive element in a direction opposite to thedirection of suction of the first-mentioned suction box, the secondsuction box being operable to draw in the photosensitive element alongthe inner wall of the box during the advance of the element.

4. The electrophotographic copier as set forth in claim 1 wherein thedrive means for the photosensitive element comprises a guide roller forpassing the photosensitive element thereon to define the path of advanceof the same and a drive roller for defining the movement of thephotosensitive element in cooperation with the roller.

5. The electrophotographic copier as set forth in claim 1 wherein thephotosensitive element is a roll of flexible sheet having an unused rollportion accommodated in a stock roller mounted at the inlet portion ofthe suction box, another portion in use one end of which is fixedlysupported on the stock roller and a used roll portion wound up on atake-up roller, the other end of the portion in use being fixedlysupported on the take-up roller.

6. The electrophotographic copier as set forth in claim 5 wherein thetake-up roller is rotatably supported on the frame of the copier and isso biased all the time as to wind up the photosensitive element in adirection opposite to the direction of suction of the suction box.

7. The electrophotographic copier as set forth in claim 5 wherein thetake-up roller is mounted at an inlet portion of a second suction boxexerting suction on the photosensitive element in a direction oppositeto the direction of suction of the first-mentioned suction box.

1. An electrophotographic copier of the image transfer type comprising:a photosensitive element made of a flexible sheet to be used repeatedlyby being driven reciprocally for each image transfer cycle, a suctionbox having means for securing one end of the photosensitive element toits inlet portion and subjected to a reduced pressure in its interior bypressure reducing means, the suction box being operable to eXert suctionon the photosensitive element to draw in the element along the innerwall of the box upon actuation of the pressure reducing means and tothereby tension the element to a planar form at an exposure station,means for fixedly supporting the other end of the photosensitiveelement, drive means for advancing the photosensitive element along apredetermined path extending through the exposure station, means forelectrostatically charging a face of the photosensitive element,exposure means for forming an image of an original on the charged faceof the photosensitive element in the exposure station forward of thecharging means to form a latent electrostatic image of the original onthe photosensitive element face, and means for transferring said latentelectrostatic image from said photosensitive element to a substrateexposed to said latent electrostatic image on said photosensitiveelement face, said charging means, exposure means and transfer meansbeing actuated during the advance of the photosensitive element.
 2. Theelectrophotographic copier as set forth in claim 1 wherein the means forfixedly supporting the other end of the photosensitive element comprisesa take-up roller so biased all the time as to wind up the photosensitiveelement in a direction opposite to the direction of suction of thesuction box.
 3. The electrophotographic copier as set forth in claim 1wherein the means for fixedly supporting the other end of thephotosensitive element comprises a second suction box having means forsecuring the other end of the photosensitive element to its inletportion and subjected to a reduced pressure in its interior by pressurereducing means for exerting suction on the photosensitive element in adirection opposite to the direction of suction of the first-mentionedsuction box, the second suction box being operable to draw in thephotosensitive element along the inner wall of the box during theadvance of the element.
 4. The electrophotographic copier as set forthin claim 1 wherein the drive means for the photosensitive elementcomprises a guide roller for passing the photosensitive element thereonto define the path of advance of the same and a drive roller fordefining the movement of the photosensitive element in cooperation withthe roller.
 5. The electrophotographic copier as set forth in claim 1wherein the photosensitive element is a roll of flexible sheet having anunused roll portion accommodated in a stock roller mounted at the inletportion of the suction box, another portion in use one end of which isfixedly supported on the stock roller and a used roll portion wound upon a take-up roller, the other end of the portion in use being fixedlysupported on the take-up roller.
 6. The electrophotographic copier asset forth in claim 5 wherein the take-up roller is rotatably supportedon the frame of the copier and is so biased all the time as to wind upthe photosensitive element in a direction opposite to the direction ofsuction of the suction box.
 7. The electrophotographic copier as setforth in claim 5 wherein the take-up roller is mounted at an inletportion of a second suction box exerting suction on the photosensitiveelement in a direction opposite to the direction of suction of thefirst-mentioned suction box.
 8. An electrophotographic copier of theimage transfer type comprising: a photosensitive element made of aflexible sheet to be used repeatedly by being driven reciprocally foreach image transfer cycle, a suction box having means for securing oneend of the photosensitive element to its inlet portion and subjected toa reduced pressure in its interior by pressure reducing means, thesuction box being operable to exert suction on the photosensitiveelement to draw in the element along the inner wall of the box uponactuation of the pressure reducing means and to thereby tension theelement to a planar form at an exposure station, means for fixedlysupporting the otHer end of the photosensitive element, drive means foradvancing the photosensitive element along a predetermined pathextending through the exposure station, means for electrostaticallycharging a face of the photosensitive element, exposure means forforming an image of an original on the charged face of thephotosensitive element in the exposure station forward of the chargingmeans to form a latent electrostatic image of the original on thephotosensitive element face, means for applying a toner to theelectrostatic image carrying photosensitive element face to form a tonerimage, and means for transferring said toner image from saidphotosensitive element to a substrate exposed to said latent toner imageon said photosensitive element face, said charging means, exposure meansand transfer means being actuated during the advance of thephotosensitive element.
 9. The electrophotographic copier as set forthin claim 8 wherein the means for fixedly supporting the other end of thephotosensitive element comprises a take-up roller so biased all the timeas to wind up the photosensitive element in a direction opposite to thedirection of suction of the suction box.
 10. The electrophotographiccopier as set forth in claim 8 wherein the means for fixedly supportingthe other end of the photosensitive element comprises a second suctionbox having means for securing the other end of the photosensitiveelement to its inlet portion and subjected to a reduced pressure in itsinterior by pressure reducing means for exerting suction on thephotosensitive element in a direction opposite to the direction ofsuction of the first-mentioned suction box, the second suction box beingoperable to draw in the photosensitive element along the inner wall ofthe box during the advance of the element.
 11. The electrophotographiccopier as set forth in claim 8 wherein the drive means for thephotosensitive element comprises a guide roller for passing thephotosensitive element thereon to define the path of advance of the sameand a drive roller for defining the movement of the photosensitiveelement in cooperation with the roller.
 12. The electrophotographiccopier as set forth in claim 8 wherein the photosensitive element is aroll of flexible sheet having an unused roll portion accommodated in astock roller mounted at the inlet portion of the suction box, anotherportion in use one end of which is fixedly supported on the stock rollerand a used roll portion wound up on a take-up roller, the other end ofthe portion in use being fixedly supported on the take-up roller. 13.The electrophotographic copier as set forth in claim 12 wherein thetake-up roller is rotatably supported on the frame of the copier and isso biased all the time as to wind up the photosensitive element in adirection opposite to the direction of suction of the suction box. 14.The electrophotographic copier as set forth in claim 12 wherein thetake-up roller is mounted at an inlet portion of a second suction boxexerting suction on the photosensitive element in a direction oppositeto the direction of suction of the first-mentioned suction box.